PML Mutation in PML-Rarα Alters PML Nuclear Body Organization and Induces ATRA Resistance in Acute Promyelocytic Leukemia

Acute promyelocytic leukemia (APL) has become a highly curable disease using target drugs including all-trans retinoic acid (ATRA) and arsenic trioxide (ATO) with or without chemotherapy. However, APL patients with acquiredPML mutationsin PML-RARα had dismal outcomes and showed resistance not only to ATO but also to ATRA.In this study, we confirmed in the clinic that APL patients with mutations in the PML moiety of PML-RARα showed different resistanceto ATRA (cross-resistance). We demonstrated that critical mutations are responsible for this "cross-resistance". Super-resolution microscopy and electron microcopy were employed to examine the fine structural changes of PML/PML-RARα nuclear bodies (NBs) in response to therapy. We observed drug-induced acceleration of NB movement, which was absent in the mutant cells. Furthermore, NB doublets were revealed, and fusion events were captured upon drug treatment. We proposed that SUMOylation contributed to increased NB dynamics, leading to more fusion incidents and thustaking functional NBs for oncoprotein degradation. Different protein density in the mutant NBswas identified by single molecule quantification, indicating reduced permeability and recruitment of clients. Taken together, our results revealed that critical sites in the PML moiety of the PML-RARα fusion gene disrupted NB scaffold organization and perturbed fusion protein degradation in response to ATRA.Our work will largely improve the mechanistic understandings of APL pathology and therapy and will shed new light on unveiling the structure and function of PML NBs.